Biomedical Engineering Reference
In-Depth Information
Q
1
Q
2
R
2
R
1
Q
3
R
3
Origin
R
4
Q
4
Figure 1.9
Generalized electric dipole
This is consistent with the elementary definition given above; in the case of two equal and
opposite charges
Q
a distance
d
apart, the electric dipole moment has magnitude
Qd
and points from the negative charge to the positive. The generalization to
n
charges is
obvious: we substitute
n
for 4 in the above definition.
There are several general rules about electric moments of charge distributions, and we
can learn a couple of the ones that apply to dipole moments by considering the simple
arrays shown in Figure 1.10 and keeping the definitions in mind.
+
Q
and
−
+
Q
(1)
+
Q
-
Q
+
Q
+
Q
(2)
(3)
+
Q
+2
Q
+
Q
+
Q
-2
Q
+
Q
(4)
(5)
+
Q
-4
Q
+
Q
+
Q
+
Q
(6)
Figure 1.10
Simple arrays of point charges
